Introduction to Marine Botany

Marine Botany is the study of aquatic plants and algae that live in oceans, seas, intertidal zones and even in brackish water (more saline than freshwater but less saline than true marine environments) of estuarine zones. It is a combined branch of marine biology and botany.

Definition from Wikipedia, Marine botany is the study of flowering vascular plant species and marine algae that live in shallow seawater of the open ocean and the littoral zone, along shorelines of the intertidal zone and coastal wetlands, even in low-salinity brackish water of estuaries.1

Regarding the oceans, the Earth is a unique planet within our solar system for a number of reasons…..

  • The Earth has water which is essential for the survival of all living beings and so far it is the only planet with life.
  • The Ocean covers a large portion of biosphere, over 71% (360 million km2 ) of Earth’s surface with an average depth of 4 km.
  • 99% of the water  in the universe is either marine or frozen,  less than 1% (0.4%) being fresh water.

Marine Environment is highly diverse. Because,

  • Marine ecosystems are hot spots for  the diversity of flora and fauna.
  • It has a greater role in the biogeochemical cycle and maintenance of atmospheric balance is played by the oceans.
Map of earth’s oceans and continents. Click the image to enlarge it. Source here.

Now, let’s know about the seven continents and how much area they cover in the global surface.

Continent Area (km2)
Asia 4,38,20,000
Africa 3,03,70,000
Antarctica 1,37,20,000
Australia  86,00000
Europe 1,0 1,80,000
North America 2,47,09,000
South America 1,78,40,000
Total 14,92,39,000 km2

Oceans of the Earth

Name Surface Area Avg. Depth Max. Depth Water Volume Covered surface
Pacific Ocean Pacific Ocean

(Deepest and Largest Ocean)

16,52,50, 000 km2  4280 m  10911 m  71,0000,000km3 covers about 30 percent of the Earth’s surface and  46% of Earth’s water surface and its total surface area, making it larger than all of Earth’s land area combined.
Atlantic Ocean  The Atlantic Ocean is the second largest of the world’s oceans 10, 64, 60, 000 sq kilometers 3646 m  8486 m  31,04,10,900 km3  It covers approximately 20 percent of the Earth’s surface and about 29 percent of its water surface area.
Indian Ocean Indian Ocean is the third largest of world oceans  7,05,60, 000 km2 3741 m 7258 m 26,40,00000 km3 Its area represents about 14 percent of the  Earth’s surface and  19.5% of the Earth’s water surface.
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean or the Austral Ocean 2,03,27,000 sq km 3,270 m 7,236 m 7,18,00000 cubic kilometers. Its area makes up 4% of the Earth’s total surface.
The Arctic Ocean Located mostly in the Arctic north polar region 1,55,58,000 square kilometers  1,038 m The deepest point is Litke Deep in the Eurasian Basin, at 5,450 m (17,880 ft). 1,87,50,000 km3 It covers about 2.8 percent of Earth’s surface.

The Bay of Bengal

The Bay of Bengal is the northeastern arm of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and the Nicobar Islands of India. Its southern limit is a line between Sangaman Kanda, Sri Lanka and the north westernmost point of Sumatra (Indonesia). It is located between latitudes 5°N and 22°N and longitudes 80°E and 100°E.

The Bay of Bengal is the Indian Ocean’s second-largest subdivision after the Arabian Sea.

  • It is the largest water region called a bay in the world. 
  • It is one of the global 64 largest marine ecoregions.
  • It occupies an area of 21,72,000 square kilometers. 
  • Average depth 2,600 m.
  • Max. depth 4,694 m.

(via World Atlas)

Bay of Bengal and its surrounding. Source: Bay of Bengal via World Atlas.

The occurrence of marine species – both plants and animals – in the Bay of Bengal has largely been controlled by the physico-chemical properties of ocean water. Water discharges from the surrounding river catchments carry huge influx of sediments full of nutrients to the Bay, particularly along the near shore region. This has turned the Bay into a fertile marine fishing ground of the region. The near-shore up-welling zone not only has a high yield of nutrients, but also is a high primary production area for the phytoplankton and related zooplankton zones.2

Nevertheless, total biodiversity including micro and macro algae are still unknown. 

Causes of loss of biodiversity in Bay of Bengal area

Damage is caused due to coral bleaching and several anthropogenic activities like fishing, pollution, habitat alteration, introduction of exotic species and climate change.

The environment of these areas are drastically undergoing degradation. So inhabiting organisms and even micro and macro algae could possibly become extinct in the near future.

The Domains of Life

Main Article directed here.

Here, the Protista kingdom of Eukaryota domain have been shortly introduced to get an idea over general characteristics of marine flora (mainly algae).

Domain Eukaryota

Kingdom Protista

  • Includes algae, Paramecium, Protozoa and slime mold.
  • Unicellular and multicellular.
  • Nucleus and cell organelles in cytoplasm.
  • Reproduced by mitosis.
  • Autotrophs, heterotrophs.

The variety of marine plants that grow in the sea range from unicellular to multi-cellular macro-algae, to flowering plants, including sea-grasses, salt marsh plants, and mangroves. 

What are Algae?

Algae  is an informal term for a large, diverse group of photosynthetic organisms 

  • They are polyphyletic. 
  • Range from unicellular genera to multi-cellular forms.
  • Most are aquatic and autotrophic.
  • Algae exhibit a wide range of vegetative and reproductive structures. 

Phylogenetically or evolutionarily speaking, Unicellular Green algae may be the ancestor of other green algae and higher plants.

Green lineages relationships or, Phylogenetic relationships among the main lineages of green plants (Leliaert et al 2012) 

Source here.
  • The divergence times are rough approximations based on the fossil record and molecular clock estimates. 

Chloroplast Evolution

Green plastid results from a primary endosymbiotic event between a host eukayotic cell and a cyanobacterium. 

It is said that ancestor e.g. Pyramimonas or other prasinophytes would have swallowed a cyanobacterium and chosen to keep it rather than digest. 

Pyramimonas gelidicola is “phagotrophic”.   

Fossil records says that Phycoma or cyst of prasinophytes are very old. 

Primary Production

  • Algae are photoautotrophic. 
  • We know, algae produces more than 80% O2 in this earth.


Seaweed refers to several species of macroscopic, multi-cellular marine algae.

  • The largest and most complex marine algae are called seaweeds. It includes some types of red, brown and green algae. 
  • Some tuft-forming blue-green algae are sometimes considered to be seaweed.
  • Seaweed can also be classified by ‘Usage’. 

Seaweeds in the Global Perspective

  • Seaweed’s appearance somewhat resembles non-arboreal terrestrial plants.
  • Algae base dynamic species counts shows that there are about 10,000 species of seaweeds, of which 6,500 are red algae 2,000 are browns and 1,500 are greens.

Massive Marine Potential

  • More than 70% seaweed is used as food whereas alginate, carrageenan and agar use 15-20% of world seaweed production.
  • Oceans cover 71% of the earth but yield only 1.5% of our food (FAO 2012).

Marine potential is massive
The EU market for sea vegetables is growing by about 7-10% per annum.

Marine Ecology

Marine Ecology is the scientific study of marine-life habitat, populations, and interactions among organisms and the surrounding environment including physical and chemical factors that affect the ability of organisms to survive and reproduce.

Biodiversity is an unique feature of our biosphere, sustainability of which is directly related to the existence of human civilization.

References & Other Links

Revised By

  • Abulais Shomrat on 21 June, 2021.
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About Abulais Shomrat

Abulais Shomrat
Currently in 4th year (Hons) in the Department of Botany, University of Dhaka. Planned to have multiple careers one by one but promised to be with 'Plantlet' as long as it's primary stage remains unfinished. Email: abulaisshomrat@gmail.com Minimum monthly resolution - Publish (1), Revise (3), Share (5)

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